Non-Patent Literature 1 specifies the functional architecture of a packet switching domain of the Third Generation Partnership Project (3GPP), which is an Evolved Packet System (EPS). To be specific, Non-Patent Literature 1 specifies various procedures for mobility management, session management and handover of mobile terminals in the EPS, including Attach procedure, Tracking Area Update (TAU) procedure, Service Request procedure, S1 Release procedure, Globally Unique Temporary Identity (GUTI) Reallocation procedure, Detach procedure, Dedicated bearer activation procedure, Bearer modification procedure, X2-based handover procedure and S1-based handover procedure.